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Scripps: Climate change, water use threaten Lake Mead, Lake Powell

February 24, 2008

Climate change, reservoir evaporation and increased water use are taxing the Colorado River system, jeopardizing a major water source for millions of people in the southwestern U.S., according to researchers at Scripps Institution of Oceanography, University of California, San Diego.

The researchers warn that the combination of human and natural forces are creating a net deficit of nearly 1 million acre-feet of water per year from the Colorado River system. Research marine physicist Tim Barnett and climate scientist David Pierce cite a 50 percent chance that Lake Mead will be dry by 2021 if current climate and water use trends continue. An unusually dry year or sustained drought would mean unstable and variable water deliveries for a system that relies on the huge reservoirs Lake Mead in Arizona/Nevada and Lake Powell in Arizona/Utah.

An analysis of U.S. Bureau of Reclamation records of past water demand, and calculations of scheduled water allocations and climate conditions, indicate that the system could run dry even if proposed mitigation measures are implemented.

“We were stunned at the magnitude of the problem and how fast it was coming at us,” said Barnett. “It’s likely to mean real changes to how we live and do business in this region,” added Pierce.

The Colorado River system includes aqueducts that carry water to Las Vegas, Los Angeles, San Diego and other Southwest communities. Because of a recent stretch of dry years, the system is only at half capacity. The researchers estimate that the system has already entered an era of deficit.

“When expected changes due to global warming are included as well, currently scheduled depletions are simply not sustainable,” wrote Barnett and Pierce in a paper, “When will Lake Mead go dry?”

They pointed out that recent studies estimate that climate change will lead to reductions in runoff to the Colorado River system. Those analyses consistently forecast reductions of between 10 and 30 percent over the next 30 to 50 years, which could affect the water supply of between 12 and 36 million people.

The researchers estimated that there is a 10 percent chance that Lake Mead could be dry by 2014. They further predict that there is a 50 percent chance that reservoir levels will drop too low to allow hydroelectric power generation by 2017.

They added that even if water agencies follow current drought contingency plans, it might not be enough to counter natural forces, especially if the region enters a period of sustained drought and/or human-induced climate changes occur as predicted.

While the researchers chose to go with conservative estimates of the water situation in their analysis, the water shortage is likely to be more serious. The team based its findings on the premise that climate change effects only started in 2007, though most researchers consider human-caused changes in climate to have likely started decades earlier. They also based their river flow on averages over the past 100 years, even though it has dropped in recent decades. Over the past 500 years the average annual flow is even less.

“Today, we are at or beyond the sustainable limit of the Colorado system,” the researchers concluded. “The alternative to reasoned solutions to this coming water crisis is a major societal and economic disruption in the desert southwest; something that will affect each of us living in the region.”